This invention relates to laser fusion targets and more particularly to a nondestructive method for determining the deuterium and tritium content of such targets.
Hollow, spherical, DT-gas-filled targets with diameters ranging from 30 to greater than 200 .mu.m and with contained fuel pressures varying from 10 to 1000 atm (at 298 K) are of interest for laser fusion. Presently, the primary gas-containment vessels of these targets are either glass microballoons or compositemetal microballoons made by electroless nickel plating of commercially available nickel/manganese/silicon alloy microballoon mandrels. These mandrels are sold under the tradename Solacells by the Solar Division of International Harvester Co., San Diego, CA.
The targets are filled by diffusing DT fuel gas through the walls at elevated temperatures, taking advantage of the exponential temperature dependence of the permeability to allow the gas to be retained for useful times at room temperature. Thus, when the microballoons are placed in a deuterium andd tritium gas mixture of a desired ratio at high pressure and elevated temperature, the deuterium and tritium readily enter the microballoons and equilibrate to the surrounding gas pressure. When the microballoons are cooled to room temperature, the diffusion rate through their walls is greatly reduced, so that the DT mixture within the microballoons remains at high pressure for times which permit useful storage before the targets are irradiated by the laser. However, because the probability of occurrence of submicroscopic pores and other defects in the walls of the microballoons is rather high, the permeation rates of the DT through the walls can vary substantially at room temperature. Accordingly, it is highly desirable to have some means for nondestructively verifying that any particular microballoon laser target does indeed contain the desired amount of DT fuel gas.